Package of two commercial grade prefilters for F300, F50F, F58F electronic air filters, two of which are used in Honeywell 20-inch x 25-inch air cleaners. Only one prefilter is needed for 20-inch x 12½-inch air cleaners. Prefilters generally do not wear out but replacement may be needed as woven aluminum foil corrodes over time. Fits F300E1035, F300A2025, F50F1065, F58F1000, F300A2012, F300B2012, F50F1040 and F50F1057 air cleaners. This prefilter is for the F300E,A; F50F; and F58F and will not fit F50A or F50E series.